U.S. patent number 5,865,927 [Application Number 08/826,991] was granted by the patent office on 1999-02-02 for process for coating hot melt adhesives.
This patent grant is currently assigned to National Starch and Chemical Investment Holding Corporation. Invention is credited to Stephen Hatfield, Paul Puletti.
United States Patent |
5,865,927 |
Puletti , et al. |
February 2, 1999 |
Process for coating hot melt adhesives
Abstract
Hot melt adhesive masses are provided with a tackless surface by
a process which comprises the steps of: a) extruding the hot melt
adhesive through an appropriate die orifice; b) spraying the
surface of the extruded adhesive with a molten film forming low
molecular weight polymer or formulated polymeric material, the
material being selected so that it will not appreciably detract
from the properties of the adhesive composition when remelted
therewith; c) heating the surface of the coated adhesive at a
temperature and for a period of time sufficient to re-melt the film
forming polymer so as to form a continuous coating thereof yet
insufficient to appreciably melt the adhesive; and d) cooling the
thus coated adhesive mass to a temperature suitable for
handling.
Inventors: |
Puletti; Paul (Pittstown,
NJ), Hatfield; Stephen (Somerville, NJ) |
Assignee: |
National Starch and Chemical
Investment Holding Corporation (Wilmington, DE)
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Family
ID: |
23027089 |
Appl.
No.: |
08/826,991 |
Filed: |
February 24, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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269402 |
Jun 30, 1994 |
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Current U.S.
Class: |
156/244.11;
264/177.17; 264/210.3; 427/372.2; 264/211.2; 427/374.1; 427/384;
427/374.2; 427/374.4 |
Current CPC
Class: |
C08J
3/124 (20130101); B01J 2/003 (20130101); B01J
2/30 (20130101) |
Current International
Class: |
C08J
3/12 (20060101); B01J 2/30 (20060101); B01J
2/00 (20060101); B29C 047/00 () |
Field of
Search: |
;427/372.2,374.1,374.4,384,422,374.2
;264/211.2,210.3,177.17,178 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 258 086 |
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Oct 1990 |
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EP |
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0 469 564 |
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Feb 1992 |
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EP |
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0 557 573 A2 |
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Feb 1992 |
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EP |
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0 412 867 |
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Sep 1993 |
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EP |
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2544654 |
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Oct 1984 |
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FR |
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2801618 |
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Jan 1988 |
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FR |
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31 38 222 |
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0000 |
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DE |
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OS 3234065 |
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0000 |
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DE |
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2 248 046 |
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Apr 1974 |
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DE |
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36 25 358 |
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Dec 1975 |
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DE |
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86 28 513.0 |
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Jan 1987 |
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DE |
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87 10 132.7 |
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Oct 1987 |
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DE |
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48-103635 |
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Dec 1973 |
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JP |
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WO 94/01330 |
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Jul 1992 |
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WO |
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WO 94/13451 |
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Jun 1994 |
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WO |
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Other References
"Nordson Hot Melt Continuous Coating System", 1992, Bulletin,
Nordson Corporation, Amherst, Ohio..
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Primary Examiner: Buffalow; E. Rollins
Attorney, Agent or Firm: Dec; Ellen T.
Parent Case Text
This application is a continuation of application Ser. No.
08/269,462, filed Jun. 30, 1994, now abandoned.
Claims
We claim:
1. A process for providing hot melt adhesive masses with a tackless
surface comprising the steps of:
a) extruding the hot melt adhesive through an appropriate die
orifice;
b) spraying the surface of the extruded adhesive with a molten film
forming polymeric material, the material being selected so that it
will not detract from the properties of the adhesive composition
when remelted therewith when such remelted adhesive is applied
through narrow orifice spray equipment;
c) heating the surface of the coated adhesive at a temperature and
for a period of time sufficient to re-melt the film forming polymer
so as to form a continuous coating thereof yet insufficient to melt
the adhesive;
d) cooling the thus coated adhesive mass to a temperature suitable
for handling; and
e) subsequently remelting the coated adhesive mass.
2. The process of claim 1 wherein the film-forming material is
selected from the group consisting of cracked linear low desity
polyethylene, high melt index ethylene vinyl acetate copolymers
containing 8 to 28% vinyl acetate, and ethylene iso-butylene
copolymers.
3. The process of claim 1 wherein the film-forming material is
selected from the group consisting of A-B-A block copolymers, lower
melt index ethylene vinyl acetate copolymers and higher molecular
weight low melt index polyethylene and polyamides which polymers
are further formulated with tackifying resins, waxes, plasticizers
and other non-tacky agents which serve to lower the coating
viscosity and improve the barrier function of the coating.
4. The process of claim 1 wherein the film-forming material is
applied by spraying in an amount sufficient to provide a coating of
0.5 to 10 mils.
5. The process of claim 1 wherein the heating operation is carried
out by flash heating at a temperature of 350.degree. to 500.degree.
F. for 1 to 10 seconds.
6. A process for providing hot melt adhesive masses with a tackless
surface comprising the steps of:
a) extruding the hot melt adhesive through an appropriate die
orifice;
b) spraying the surface of the extruded adhesive with a molten film
forming polymeric material, the material being such that it will
not detract from the properties of the adhesive composition when
remelted therewith and being selected from the group consisting of
cracked linear low density polyethylene, high melt index ethylene
vinyl acetate copolymers containing 8 to 28% vinyl acetate,
ethylene iso-butylene copolymers, A-B-A block copolymers, lower
melt index ethylene vinyl acetate copolymers and higher molecular
weight low melt index polyethylene and polyamides which polymers
are further formulated with at least one of a member selected from
the group consisting of tackifying resins, waxes, and
plasticizers;
c) heating the surface of the coated adhesive at a temperature and
for a period of time sufficient to re-melt the film forming polymer
so as to form a continuous coating thereof yet insufficient to melt
the adhesive when said remelted adhesive is applied through narrow
orifice spray equipment;
d) cooling the thus coated adhesive mass to a temperature suitable
for handling; and
e) subsequently remelting the coated adhesive mass.
Description
BACKGROUND OF THE INVENTION
This invention relates to a method for coating hot melt adhesives
compositions to provide tack free surfaces.
Hot melt adhesives which are generally applied while in the molten
or liquid state are solid at room temperature. Typically, these
adhesives are provided in the form of blocks and because of the
nature of these materials, particularly the pressure sensitive hot
melts, there are problems associated with handling and packaging
them. The solid adhesive blocks not only stick or adhere to hands
or mechanical handling devices and to each other, but they also
pick up dirt and other contaminants. Additionally, certain
applications which require high tack formulations result in blocks
that will deform or cold flow unless supported during shipment. The
need and advantages for providing tackless or non-blocking hot melt
adhesives are apparent and various ways of accomplishing this have
been developed.
Japanese Patent 48-103635 published Dec. 26, 1973, discloses a
granular adhesive which is tacky at room temperature and coated or
enveloped with a non-tacky hot meltable material that is the same
type or is miscible or mixable with it.
French Patent 2,544,654 published Oct. 26, 1984, discloses forming
a tackless hot melt by adding molten hot melt to a mold containing
a preformed support layer having a transfer film thereon which is
compatible with the hot melt.
U.S. Pat. Nos. 4,748,796 issued Jun. 12, 1988, and 4,755,245 issued
Jul. 5, 1988, disclose forming a protective coating for an adhesive
material by electrostatically coating a mold or cavity with a
powder screen and then pouring hot melt into the mold.
French Patent 2,601,616 published Oct. 22, 1988, discloses forming
blocks of hot melt pressure sensitive adhesives by casting the
pressure sensitive adhesive into molds precoated by spraying with a
film of non self-sticking hot melt material thereby forming a
fusible non-tacky veil around the pressure sensitive block.
In German Patent 22 48 046 and U.S. Pat. 4,054,632 the hot melt
adhesive is squeeze-cut into pillow-shaped pieces; the pieces
subsequently cooled and solidified.
European Patent 412,867 published Feb. 13, 1991, discloses a
process for coating hot melt adhesives with a compatible
anti-adhesive agent, the coating being done at a temperature higher
than its softening point.
Still other processes involve the coextrusion of a sheath
surrounding the hot-melt material where the coextruded material may
be, for example, polyethylene or a non-self-adhesive "hot-melt"
compatible with the formulation of the extruded product.
SUMMARY OF THE INVENTION
In accordance with the present invention, hot melt adhesive masses
are provided with a tackless surface by a process which comprises
the steps of:
a) extruding the hot melt adhesive through an appropriate die
orifice;
b) spraying the surface of the extruded adhesive with a molten film
forming low molecular weight polymer or formulated polymeric
material, the material being selected so that it will not
appreciably detract from the properties of the adhesive composition
when remelted therewith;
c) heating the surface of the coated adhesive at a temperature and
for a period of time sufficient to re-melt the film forming polymer
so as to form a continuous coating thereof yet insufficient to
appreciably melt the adhesive; and
d) cooling the thus coated adhesive mass to a temperature suitable
for handling.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated by the accompanying FIGURE. In the
FIGURE, 1 represents the extruder, 2 the extruder screw(s), 3 the
hot melt adhesive, 4 the spray of the polymeric coating, 5 the heat
treatment and 6 the cooling water bath.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The method of the present invention is adaptable to the packaging
of virtually any type of hot melt adhesive composition. As examples
the method disclosed herein may be used to package hot melt
adhesives prepared from polymers and copolymers of synthetic
resins, rubbers, polyethylene, polypropylene, polyurethane,
acrylics, vinyl acetate, ethylene vinyl acetate and polyvinyl
alcohol. More specific examples include hot melt adhesives prepared
from the following:
a. rubber polymers such as block copolymers of monovinyl aromatic
hydrocarbons and conjugated diene, e.g., styrene-butadiene,
styrene-butadiene-styrene, styrene-isoprene-styrene,
styrene-ethylene-butylene-styrene and styrene-ethylene
propylene-styrene;
b. ethylene-vinyl acetate polymers, other ethylene esters and
copolymers, e.g., ethylene methacrylate, ethylene n-butyl acrylate
and ethylene acrylic acid;
c. polyolefins such as polyethylene and polypropylene;
d. polyvinyl acetate and random copolymers thereof;
e. polyacrylates;
f. polyamides;
g. polyesters;
h. polyvinyl alcohols and copolymers thereof;
i. polyurethanes;
j. polystyrenes;
k. polyepoxides;
l. graft copolymers of vinyl monomer(s) and polyalkylene oxide
polymers; and
m. aldehyde containing resins such as phenol-aldehyde,
urea-aldehyde, melamine-aldehyde and the like.
Most often such adhesives are formulated with tackifying resins in
order to improve adhesion and introduce tack into the adhesive.
Such resin include, among other materials, (a) natural and modified
resins, (b) polyterpene resins, (c) phenolic modified hydrocarbon
resins, (d) coumaroneindene resins, (e) aliphatic and aromatic
petroleum hydrocarbon resins, (f) phthalate esters and (g)
hydrogenated hydrocarbons, hydrogenated rosins and hydrogenated
rosin esters.
Desirable optional ingredients include diluents, e.g., liquid
polybutene or polypropylene, petroleum waxes such as paraffin and
microcrystalline waxes, polyethylene greases, hydrogenated animal,
fish and vegetable fats, mineral oil and synthetic waxes as well as
hydrocarbon oils such as naphthionic or paraffinic mineral
oils.
Other optional additives may include stabilizers, antioxidants,
colorants and fillers. The selection of components and amounts as
well as the preparation thereof are well known in the art and
described in the literature.
The adhesives to be treated in accordance with the invention are
generally melt blended in a mixer/extruder and then extruded
through an appropriately sized orifice while still at a temperature
above the softening point of the adhesive. The die in the orifice
may be of any conventional configuration and generally are such as
to provide either a slat-like or cord-like configuration.
As the hot melt adhesive is extruded, it is spray coated with the
film forming material. Any non-tacky film forming material which
has a relatively low molecular weight and which will be compatible
with, and not appreciably detract from the properties of, the
adhesive when remelted may be utilized herein. In general, we have
found that the most satisfactory materials have a viscosity less
than 10,000 cps, and preferably less than 2000 cps., at the
temperature at which they are sprayed (e.g., about 350.degree. F.)
Suitable film-forming materials include, for example, (a) cracked
linear low density polyethylene such as Eastman's Epolene C-10, (b)
high melt index ethylene vinyl acetate (8-28% vinyl acetate)
copolymer such as Elvax 410 (18% vinyl acetate) or Elvax 205 (28%
vinyl acetate), both from Du Pont and (c) ethylene iso-butylene
copolymers such as DP 8910 from Shell (6% ethylene). Due to the
high molecular weight of these polymers and resultant higher
relative viscosity, increased re-flow temperatures are required
making these polymers more useful in the packaging of higher
softening point products. For this reason it is often beneficial to
use formulated materials which are based on even higher molecular
weight polymers such as A-B-A block copolymers, most commonly of
the type where A is styrene and B is isoprene or butadiene or
hydrogenated derivatives thereof; lower melt index ethylene vinyl
acetate; or higher molecular weight low melt index polyethylene and
polyamides; which polymers are then formulated with tackifying
resins, waxes, plasticizers and other non-tacky agents which serve
to lower the coating viscosity and improve the barrier function of
the coating.
The coating step may be performed directly from the extruder while
the adhesive is still at a relatively elevated temperature or the
adhesive extrudate may be cooled and subsequently coated with the
non-tacky material. Due to the difficulty in handling the uncoated
adhesive mass, coating directly from the extruder is preferred.
The material is sprayed at a rate sufficient to provide a coating
of 0.5 to 10 mils, preferably 1 to 3 mils thickness. In order to
achieve a relatively uniform spray pattern, it is preferred to use
equipment which is capable of coating the entire circumference of
the extrudate in one step. Suitable equipment for such spray
application of 100% solid material is available from Nordson.
Subsequent to the spray coating, it is an essential feature of the
invention that the coated adhesive be subjected to a heating
operation wherein the exterior film forming material is exposed to
temperatures in excess of its melting point so it will reflow and
provide a uniform coated surface. In so doing, it is also important
that the heating temperature and time not substantially interfere
with the configuration of the adhesive core material. In general,
flash heating at temperatures of 350.degree. to 500.degree. F. for
periods of time of 1 to 10 seconds is preferred. This step may also
be carried out using the Nordson coating equipment.
Following the reheating step, the coated adhesive mass is then
cooled for handling. The mass could be allowed to cool under
ambient conditions, however it is preferred that the cooling occur
in a water bath or in a refrigerant medium such as chilled glycol,
liquid or gaseous nitrogen, compressed carbon dioxide or the
like.
The coated extrudate can be cut mechanically into desired size
portions using conventional equipment such as water jet, laser, or
hot knife, if desired in conjunction with a voider roll.
The resultant coated hot melt adhesive may be further packaged in a
container to reduce its exposure to the environment, moisture or
other contaminants. The container or other wrappings would then be
removed by conventional procedures prior to utilization of the hot
melt adhesive.
EXAMPLE
The adhesive raw materials are compounded in a conventional twin
screw extruder (length/diameter ratio of 30:1 to 50:1). From the
extruder die head, the material is filtered through a 75 micron
screen pack at a temperature of 180.degree. C..+-.30.degree. C. The
molten material is fed to a gear pump which pumps the material
through a tube into a shell heat exchanger to lower the temperature
to a point at which it can be shaped. The material is then pushed
through a circular die having an internal diameter approximately
the size of the desired package. The formed material is then passed
vertically through the Nordson container coating system in order to
apply a coating of approximately 3 mils to the hot melt adhesive.
The coated material is then reheated to reflow for a period of
about 2 seconds. In the case of formulated coatings prepared from a
molten blend of 35% Escorez 5320 (Exxon), 15% Kraton G 1652
(Shell), 10% Kraton 1657 (Shell), and 40% paraffin wax, reflow
occurs at about 375.degree. F. If a coating comprising 40% Elvax
260 (Du Pont), 40% paraffin wax and 20% Wingtac Extra (Goodyear) is
used, temperatures of about 450.degree. F. are need to reflow.
The resultant coated hot melt adhesive package is passed through
voider rolls and cut into appropriate size segments which are then
cooled in a water bath to ensure adequate solidification of the
internal core material.
This process provides hot melt adhesives having a continuous tack
free coating which can be added directly to the melt pot and will
remelt and be readily incorporated into the molten hot melt for
application through conventional equipment including narrow orifice
spray equipment.
* * * * *